Remember when Audi planned a diesel V12 R8 supercar?

Remember 2008? A president called Obama, a chap named Lewis Hamilton winning his first F1 title, and meanwhile, the car industry worshipped at the altar of diesel. Tax breaks were built around its lo-CO2 habits. It’d conquered everything from the once exclusively-petrol Range Rover segment to the diminutive Smart ForTwo city car. And at Le Mans, Audi was on a three-year winning-streak with the R10 TDI: the first turbodiesel machine ever to come home first at the world’s most illustrious 24-hour race.

Diesel meant range, torque, and at last, high-performance. Modern diesel engines were smooth enough to power high-end cars without invoking agricultural equipment comparison. Enter Audi, keen to draw up a link between its Le Mans hat trick and its road cars, hatching a plot to create a shock new niche-buster. The world’s first diesel-powered supercar.

Back in 2008, the R8 was new on the scene and continuing to bowl reviewers over with the savage noise of its 4.2-litre naturally aspirated V8, its playful balance, and how darn exotic the thing looked. There was no doubt Audi had made a credible, desirable junior supercar. The ideal platform for diesel to reach new heights of silliness.

At the time, the VW Group’s flagship diesel was a 5.0-litre V10 TDI that’d seen duty in the Volkswagen Touareg. Audi’s engineers, keen to one-up the parent brand, had been beavering away on a 6.0-litre, twin-turbo V12 TDI destined for service in an ultimate version of the Q7 4x4. It developed 500PS – 493bhp, in old money - and a staggering 738lb ft of torque. That’s one thousand Newton metres of twist, from 1,750rpm. Remember, this is a time before we’d all been mind-frazzled by the instant torque of a Tesla EV. Audi had a monster on its hands.

Administering this volcanic engine to an unsuspecting R8 concept car wasn’t a doddle. The V12’s block was a lot longer than the V8, so stowage space behind the R8’s seats was sacrificed. To cool the searing turbos, the car’s infamous ‘sideblade’ intakes were teased open, and a NACA duct was plumbed into the glass roof panel. Meanwhile, the front intakes are rear vents were enlarged to cope with the V12’s ravenous appetite for air to combust, or cool itself.

Despite weighing 150kg more than a conventional R8, Audi claimed the new Franken-diesel could scorch from 0-62mph in 4.2 seconds – half a second faster than the petrol version. Top speed was calculated at 193mph. And yet, 25mpg was possible in daily driving, with 30mpg on a long run mooted. All this despite maintaining the R8’s signature feature: the open-gate, six-speed manual gearbox. Audi debuted the car at the Los Angeles motor show with a 50:50 intent on a production run. Apparently, several blank-cheque offers were made for the concept itself.

We’d wager a few of those would-be buyers would’ve baulked had they realised the concept car wasn’t quite as production-ready as it looked. Unable to get the R8’s gearbox to fit in front of the gargantuan engine, engineers had pinched one from an A4. Keen students of physics will be aware than a 2008 Audi A4’s gearbox really isn’t designed with handling one thousand torques in mind. So, the mighty engine was detuned to under 400lb ft, so the fierce-looking concept didn’t detonate its transmission into shrapnel.

Despite its positive reception, the R8 V12 TDI concept remained a one-off folly. In 2009, Audi released the R8 V10, featuring a detuned 5.2-litre Lamborghini Gallardo engine and performance figures even quicker than the diesel’s. Plus, it was about £80,000 less than what the TDI would’ve cost to buy, and sounded approximately four hundred per cent more exotic.

Instead, Audi poured its alternative-fuel R8 development Euros into an electric e-tron version, which was offered for public sale in 2014, and promptly sank without trace. To this day, Audi refuses to say how many R8 e-trons it sold, preferring to class it as an engineering exercise. Which is usually code for “please don’t remind the accountants about that.”

Though the V12 diesel heart of the R8 did indeed go on to live in a short-lived Q7, that marked Peak Diesel. Since then, dieselgate has robbed turbodiesels of their political credibility, which has switched allegiance to EVs overnight.

Just about the only bit of this ballsy R8 that lived on is fixing the Engine Start and Drive Select buttons to the steering wheel – you’ll see the same detail in the new R8 V10 Plus. So, not a complete folly after all, then. Cough.